net: airoha: read default PSE reserved pages value before updating

Store the default value for the number of PSE reserved pages in orig_val
at the beginning of airoha_fe_set_pse_oq_rsv routine, before updating it
with airoha_fe_set_pse_queue_rsv_pages().
Introduce airoha_fe_get_pse_all_rsv utility routine.

Introduced by commit 23020f04 ("net: airoha: Introduce ethernet support
for EN7581 SoC")

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241001-airoha-eth-pse-fix-v2-1-9a56cdffd074@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>